1. Field of the Invention
The present invention relates generally to a method and apparatus for performing a coronary artery bypass procedure. More particularly, the present invention performs a coronary artery bypass utilizing a number of approaches including an open-chest approach (with and without cardiopulmonary bypass), a closed-chest approach under direct viewing and/or indirect thoracoscopic viewing (with and without cardiopulmonary bypass), and an internal approach through catheterization of the heart and a coronary arterial vasculature without direct or indirect viewing (with and without cardiopulmonary bypass).
2. Description of the Prior Art
Coronary artery disease is the leading cause of premature death in industrialized societies. But the mortality statistics tell only a portion of the story; many who survive face prolonged suffering and disability.
Arteriosclerosis is xe2x80x9ca group of diseases characterized by thickening and loss of elasticity of arterial walls.xe2x80x9d DORLAND""S ILLUSTRATED MEDICAL DICTIONARY 137 (27th ed. 1988). Arteriosclerosis xe2x80x9ccomprises three distinct forms: atherosclerosis, Monckeberg""s arteriosclerosis, and arteriolosclerosis.xe2x80x9d Id.
Coronary artery disease has been treated by a number of means. Early in this century, the treatment for arteriosclerotic heart disease was largely limited to medical measures of symptomatic control. Evolving methods of diagnosis, coupled with improving techniques of post-operative support, now allow the precise localization of the blocked site or sites and either their surgical re-opening or bypass.
The re-opening of the stenosed or occluded site can be accomplished by several techniques. Angioplasty, the expansion of areas of narrowing of a blood vessel, is most often accomplished by the intravascular introduction of a balloon-equipped catheter. Inflation of the balloon causes mechanical compression of the arteriosclerotic plaque against the vessel wall. Alternative intravascular procedures to relieve vessel occlusion include atherectomy, which results in the physical desolution of plaque by a catheter equipped (e.g. a cutting blade or high-speed rotating tip). Any of these techniques may or may not be followed by the placement of mechanical support and called a xe2x80x9cstent,xe2x80x9d which physically holds the artery open.
Angioplasty, and the other above-described techniques (although less invasive than coronary artery bypass grafting) are fraught with a correspondingly greater failure rate due to plaque reformation. Contemporary reports suggest re-stenosis is realized in as many as 25 to 55 percent of cases within 6 months of successful angioplasty. See Bojan Cercek et al., 68 AM. J. CARDIOL. 24C-33C (Nov. 4, 1991). It is presently believed stenting can reduce the re-stenosis rate.
A variety of approaches to delay or prevent re-blockage have accordingly evolved. One is to stent the site at the time of balloon angioplasty. Another is pyroplasty, where the balloon itself is heated during inflation. As these alternative techniques are relatively recent innovations, it is too early to tell just how successful they will be in the long term. However, because re-blockage necessitates the performance of another procedure, there has been renewed interest in the clearly longer-lasting bypass operations.
The current indications for coronary artery bypass grafting have been outlined. See LUDWIG K. VON SEGESSER, ARTERIAL GRAFTING FOR MYOCARDIAL REVASCULARIZATION: INDICATIONS, SURGICAL TECHNIQUES AND RESULTS 4-5 (1990). Criteria vary dependent upon whether the intent is therapeutic (that is, to reverse cardiac compromise in the patient currently suffering symptoms), or prophylactic (that is, to prevent a potentially fatal cardiac event from occurring in someone who is, at present, symptom free). Id.
The traditional open-chest procedure requires an incision of the skin anteriorly from nearly the neck to the navel, the sawing of the sternum in half longitudinally, and the spreading of the ribcage with a mechanical device to afford prolonged exposure of the heart cavity. If both lungs are deflated, a heart-lung, or cardiopulmonary bypass procedure, is also necessary.
Depending upon the degree and number of coronary vessel occlusions, a single, double, triple, or even greater number of bypass procedures may be necessary. Often each bypass is accomplished by the surgical formation of a seperate conduit from the aorta to the stenosed or obstructed coronary artery, at a location distal to the diseased site. A major obstacle has been the limited number of vessels that are available to serve as conduits. Potential conduits include the two saphenous veins of the lower extremities, the two internal thoracic arteries under the sternum, and the single gastroepiploic artery in the upper abdomen. Theoretically, if all of these vessels were utilized, the procedure would be limited to a quintuple (5-vessel) bypass. Because of this, newer procedures using a single vessel to bypass multiple sites have evolved. However, this technique is fraught with its own inherent hazards, though. When a single vessel is used to perform multiple bypasses, physical stress (e.g., torsion) on the conduit vessel can result. Such torsion is particularly detrimental when this vessel is an artery.
Unfortunately, attempts at using vessels from other species (xenografts), or other non-related humans (homografts) has been largely unsuccessful. See LUDWIGK. VON SEGESSER, ARTERIAL GRAFTING FOR MYOCARDIAL REVASCULARIZATION: INDICATIONS, SURGICAL TECHNIQUES AND RESULTS 38-39 (1990). Similarly, trials with synthetic alternatives have not been encouraging. See Id. at 39.
While experimental procedures transplanting alternative vessels continue to be performed, in general clinical practice there are five vessels available to use in this procedure over the life of a particular patient. Once these xe2x80x9csparexe2x80x9d vessels have been sacrificed, there is little or nothing that modern medicine can offer. It is unquestionable that new methods, not limited by the availability of such conduit vessels, are needed.
In the past, the normal contractions of the heart have usually been stopped during suturing of the bypass vasculature. This can be accomplished by either electrical stimulation which induces ventricular fibrillation, or through the use of certain solutions, called cardioplegia, which chemically alter the electrolytic milleau surrounding cardiac muscles. Stoppage of the heart enhances visualization of the coronary vessels, while removing the need for blood flow through the coronary arteries during the procedure. This provides the surgeon with a xe2x80x9cdry fieldxe2x80x9d in which to operate and create a functional anastomosis. After the coronary artery bypass procedure is completed, cardioplegia is reversed, and the heart electrically stimulated if necessary. As the heart resumes the systemic pumping of blood, the cardiopulmonary bypass is gradually withdrawn. The separated sternal sections are then re-joined, and the overlying skin and saphenous donor site or sites (if opened) are sutured closed.
The above-described procedure is highly traumatic. Immediate post-operative complications include infection, bleeding, renal failure, pulmonary edema and cardiac failure. The patient must remain intubated and under intensive post-operative care. Narcotic analgesia is necessary to alleviate the pain and discomfort.
The most troubling complication, once the immediate post-surgical period has passed, is bypass vessel re-occlusion. This has been a particular problem with bypass grafting of the left anterior descending coronary artery when the saphenous vein is employed. Grafting with the internal thoracic (internal mammary) artery results in long-term patency rate superior to saphenous vein grafts, particularly when the left anterior descending coronary artery is bypassed. Despite this finding, some cardiothoracic surgeons continue to utilize the saphenous vein because the internal thoracic artery is smaller in diameter and more fragile to manipulation; thus making the bypass more complex, time-consuming, and technically difficult. Additionally, there are physiological characteristics of an artery (such as a tendency to constrict) which increases the risk of irreversible damage to the heart during the immediate period of post-surgical recovery.
Once the patient leaves the hospital, it may take an additional five to ten weeks to recover completely. There is a prolonged period during which trauma to the sternum (such as that caused by an automobile accident) can be especially dangerous. The risk becomes even greater when the internal thoracic artery or arteries, which are principle suppliers of blood to the sternum, have been ligated and employed as bypass vessels.
Due to the invasive nature of the above technique, methods have been devised which employ contemporary thoracoscopic devices and specially-designed surgical tools to allow coronary artery bypass grafting by closed-chest techniques. While less invasive, all but the most recent closed-chest techniques still require cardiopulmonary bypass, and rely on direct viewing by the surgeon during vascular anastomoses. These methods require a very high level of surgical skill together with extensive training. In such situations, the suturing of the bypassing vessel to the coronary artery is performed through a space created in the low anterior chest wall by excising the cartilaginous portion of the left fourth rib. Also, as they continue to rely on the use of the patient""s vessels as bypass conduits, the procedures remain limited as to the number of bypasses which can be performed. Because of these issues, these methods are not yet widely available.
In view of the above, it would be desirable to provide other methods or techniques by which adequate blood flow to the heart could be re-established which do not rely on the transposition of a patient""s own arteries or veins. It would also be desirable to provide other methods or techniques by which adequate blood flow to the heart could be re-established which results in minimal tissue injury. It would be particularly desirable if such methods or techniques did not require opening of the chest by surgical incision of the overlying skin and the division of the sternum. It would be even more desirable if such methods or techniques did not require surgical removal of cartilage associated with the left fourth rib, did not require the surgical transection of one or both internal thoracic arteries, did not require the surgical incision of the skin overlying one or both lower extremities, and did not require the surgical transection and removal of one or both saphenous veins. It would also be desirable if such methods or techniques could be performed without stoppage of the heart, and without cardiopulmonary bypass.
The conventional surgical procedures (such as those described above) for coronary artery bypass grafting using saphenous vein or internal thoracic artery via an open-chest approach have been described and illustrated in detail. See generally Stuart W. Jamieson, Aortocoronary Saphenous Vein Bypass Grafting, in ROB and SMITH""S OPERATIVE SURGERY: CARDIAC SURGERY, 454-470 (Stuart W. Jamieson and Norman E. Shumway eds., 4th ed. 1986); LUDWIGK. VON SEGESSER, ARTERIAL GRAFTING FOR MYOCARDIAL REVASCULARIZATION: INDICATIONS, SURGICAL TECHNIQUES AND RESULTS 48-80 (1990). Conventional cardiopulmonary bypass techniques are outlined in Mark W. Connolly and Robert A. Guyton, Cardiopulmonary Bypass Techniques, in HURST""S THE HEART 2443-450 (Robert C. Schlant and R. Wayne Alexander eds., 8th ed. 1994). Coronary artery bypass grafting, utilizing open-chest techniques but without cardiopulmonary bypass, is described in Enio Buffolo et al., Coronary Artery Bypass Grafting Without Cardiopulmonary Bypass, 61 ANN. THORAC. SURG. 63-66 (1996).
Some less conventional techniques (such as those described above) are performed by only a limited number of appropriately skilled practitioners. Recently developed techniques by which to perform a coronary artery bypass graft utilizing thoracoscopy and minimally-invasive surgery, but with cardiopulmonary bypass, are described and illustrated in Sterman et al., U.S. Pat. No. 5,452,733 (1995). An even more recent coronary artery bypass procedure employing thoracoscopy and minimally-invasive surgery, but without cardiopulmonary bypass, is described and illustrated by Tea E. Acuff et al., Minimally Invasive Coronary Artery Bypass Grafting, 61 ANN. THORAC. SURG. 135-37 (1996).
Methods of catheterization of the coronary vasculature, techniques utilized in the performance of angioplasty and atherectomy, and the variety of stents in current clinical have been described and illustrated. See generally Bruce F. Waller and Cass A. Pinkerton, The Pathology of Interventional Coronary Artery Techniques and Devices, in 1 TOPOL""S TEXTBOOK OF INTERVENTIONAL CARDIOLOGY 449-476 (Eric J. Topol ed., 2nd ed. 1994); see also David W. M. Muller and Eric J. Topol, Overview of Coronary Athrectomy, in 1 TOPOL""S TEXTBOOK OF INTERVENTIONAL CARDIOLOGY at 678-684; see also Ulrich Sigwart, An Overview of Intravascular Stents: Old and New, in 2 TOPOL""S TEXTBOOK OF INTERVENTIONAL CARDIOLOGY at 803-815.
Finally, some techniques remain in the experimental stages, and are limited to animal testing. Direct laser canalization of cardiac musculature (as opposed to canalization of coronary artery feeding the cardiac musculature) is described in Peter Whittaker et al., Transmural Channels Can Protect Ischemic Tissue: Assessment of Long-term Myocardial Response to Laserxe2x80x94and Needle-Made Channels, 94(1) CIRCULATION 143-152 (Jan. 1, 1996).
According to the present invention, a method and apparatus for surgically bypassing an obstructed coronary artery or arteries relies on the establishment of a channel or channels leading directly from a chamber of the heart into the obstructed coronary artery or arteries at a site or sites distal to the obstruction. At the time of, or prior to the procedure, coronary arterial obstruction can be identified through angiography. Standard angiographic techniques utilize radio-opaque dyes introduced into the coronary arterial vasculature to identify defects in blood flow by standard radiological techniques. Standard radiological techniques involve visualization of flow defects through the taking of X-rays or viewing under fluoroscopy at the time that a radio-opaque dye is injected. Alternatively, a video recording system may be enlisted to record these fluoroscopic images, and allow the identification of more subtle defects through repeated viewings. At the time of, or prior to the procedure, a site or sites for the coronary artery bypass procedure can thus be selected.
The present invention is particularly useful for coronary artery bypass procedures in a patient suffering from obstructive coronary artery disease. The methods can be performed while the patient is anesthetized. Anesthesia may be, but is not limited to, general anesthesia. The present permits an array of procedures of varying invasiveness. As in other procedures, the level of anesthesia necessary is expected to vary directly with the invasiveness of the surgery. The present invention, because it minimizes normal tissue damage, is especially useful for coronary artery bypassing in a patient who, because of other medical problems such as chronic respiratory failure, must be maintained at a higher level of consciousness than that usually realized during standard general anesthesia. In such a patient, a less invasive approach may be chosen. As in any major surgical procedure, the patient""s heart and respiratory rates, peripheral oxygenation, urinary output, and other bodily functions may be monitored. During some or all of the bypass, cardiac contractions can be slowed, or stopped, to both improve visualization of the coronary vasculature, and to reduce the oxygen requirements of cardiac muscle. An intra-esophageal probe or probes, or other appropriately-placed probe or probes to monitor the cardiac cycle, and to trigger power to the intraventricular laser when utilized, may be advantageous.
The present invention can be performed in an operating room equipped with standard X-ray, and/or fluoroscopy, and/or cine-fluoroscopy equipment, as is standardly utilized during cardiac catheterization procedures. The present invention can be performed while the treating physician or physicians view the X-rays, and/or fluoroscopic images produced during the procedure, as is standardly done during cardiac catheterization.
The present invention avoids the previous limitations on the number of performable bypass procedures. Due to the limited number of arteries and/or veins available, standard procedures become increasingly risky to repeat. Rather than relying on harvested veins and arteries as bypass conduits, the present invention forms a channel (or conduit) which leads directly from a chamber of a patient""s heart into a coronary artery at a site distal to the obstruction or narrowing.
In the most preferred embodiment, the left ventricle is the chamber of the heart utilized. There are two reasons for this selection. First, the left ventricle normally provids blood to the coronary arteries, because it pumps blood into the aorta from which the coronary arteries branch. Therefore, the blood pressure peak generated by the left ventricle is most similar to the blood pressure peak the proximal coronary artery would normally experience. Second, the blood which flows into the left ventricle is returning from the the lungs. In the lungs the blood acquires oxygen and loses carbon dioxide. Thus, the blood available by shunting from the chambers of the left side of the heart will have a higher oxygen and lower carbon dioxide content then that blood within the right-sided heart chambers.
The Open-Chest Procedure
As a first step, the patient can be prepared in the usual fashion for open-chest cardiac bypass surgery. Once access to the heart and coronary vasculature is gained, cardiopulmonary bypass and stoppage of the heart may, but is not necessarily, performed.
As a second step, blood flow through the coronary artery to be bypassed is stopped. One example by which blood flow can be stopped is by clamping the artery proximal to the chosen bypass site. Another example by which blood flow can be discontinued is by forming a loop around the artery with suture and applying traction.
As a third step, an incision is formed in the artery at a site distal to the narrowing or obstruction. A channel is then formed leading from a coronary artery through the wall of the coronary artery, through the underlying cardiac muscle and into a chamber of a heart. One example by which such a channel could be formed is by laser ablation of the intervening tissue, another example is by forming an incision with an electrosurgical tool which will simultaneously cut and cauterize the intervening tissue, and yet another example is by blunt dissection with an appropriate blunt tool such as an awl punch or trocar.
As a fourth step, one arm of an appropriately dimensioned apparatus of the present invention is inserted through this channel leading into the chamber of the heart. The remaining arm or arms of the apparatus are then seated within the lumen of the coronary artery.
Depending on the relationship over time of the pressures present within the chamber of the heart as compared to the pressures realized within the coronary artery at the bypass location, a check valve permitting unidirectional blood flow from the chamber of the heart into the coronary artery may be associated with the apparatus. The use of a check valve, and the opening pressure of such a valve when employed, can be individually determined through selective catheterization of the coronary artery and the chamber of the heart either prior to, or at the time of, the bypass procedure. See Minoru Hongo et al., Effects of Heart Rate on Phasic Coronary Blood Flow Pattern and Flow Reserve in Patients with Normal Coronary Arteries: A study with an Intravascular Doppler Catheter and Spectral Analysis, 127(3) AM. HEART J. 545-51 (March 1994) (outlining newer techniques by which pressures within the coronary artery can be measured during the normal cardiac cycle). Simultaneous electrocardiography may also be useful in this regard. Such catheterization and blood pressure measurements performed in concert with stress testing and electrocardiography can be utilized to determine what minimal pressures are necessary within the bypassed coronary artery to produce adequate blood flow at rest and during stress. Correlation of the pressure necessary within the coronary artery to that present within the chambers of the heart can be used to establish the appropriate chamber of the heart to utilize. In the most preferred embodiment, the left ventricle is anticipated.
As a fifth step, the coronary artery incision is closed in the usual fashion. One example of closure is re-approximating the walls of the coronary artery with suture, while another example is closure of the walls by staples which interlock with the underlying device of the present invention.
As a sixth step (if needed), cardiac contractions are reinitiated. One example by which cardiac contractions are commonly reinitiated is through electrical defibrillation, while another example is through the reversal of cardioplegia by standard techniques. Cardioipulmonary bypass, if utilized, can then be slowly discontinued.
As a seventh step, the pericardium, sternum, and overlying skin can then be re-approximated and sutured and/or stapled closed, as is standardly performed following open-chest surgery.
The Closed-Chest Procedure
In another embodiment, the method and apparatus of the present invention reduces trauma to normal tissue, limits blood loss, and lowers the risk of infection heretofore associated with standard coronary artery bypass procedures. In this embodiment, the procedure is performed under direct and indirect viewing through a space (i.e., window) formed in the left anterior chest wall, as well as viewed through a thoracoscope. In this embodiment, the surgery is performed through the formed window via a series of access trocar sheaths, which allow the introduction of surgical instruments. See Sterman et al., U.S. Pat. No. 5,452,733 (1995). See, also Acuff et al., Minimally Invasive Coronary Artery Bypass Grafting, 61 ANN. THORAC. SURG. 135-37 (1996). The basic steps of the procedure are similar to the open-chest technique outlined above. The location of the bypass site, the requirement for adequate visualization, and the overall health of the particular patient are factors likely to contribute to the decision as to which procedure to employ.
The Catheterization Procedure
The method and apparatus of the present invention, in yet another embodiment, greatly minimizes damage to normal tissue, although at the expense of the (at least partial) loss of direct visualization, by performing the coronary bypass surgery via catheterization. In this embodiment, the entire procedure is limited to two incisions: one in the groin and one in the right superior-anterior chest. Catheter access to the coronary arterial vasculature and chambers of the heart are achieved through these incisions.
As a first step, the obstructed coronary artery is catheterized by introduction of a catheter into the innominate or femoral artery and by the feeding of the catheter retrograde through the ascending aorta and into the obstructed artery via standard catheterization techniques. If the obstruction does not allow passage of the catheter past the site or sites of obstruction, the catheter can be removed, and angioplasty, atherectomy, or another appropriate procedure can be performed. Once the catheter is positioned distally to the site of the obstruction, a stent is secured to the arterial wall at the pre-selected bypass site. This can be accomplished by inflation of a balloon circumferentially attached to the catheter. This stent provides the appropriate structural strength to ensure continued integrity of the coronary artery, following opening of the coronary arterial wall. Once this stent has been placed, the catheter is withdrawn and allowed to rest within the ascending aorta.
As a second step, a chamber of a heart is catheterized. The left side of the heart, including the left auricle and left ventricle, can be catheterized by introduction of a penetration means (e.g., laser or radiofrequency) equipped catheter into the innominate or femoral artery and by the feeding of said catheter retrograde through the ascending aorta and into said left auricle or left ventricle via standard catheterization techniques. In the preferred embodiment, the left ventricle is catheterized in this manner. In one embodiment, a channel, leading from one of the chambers of the left side of a heart and continuing through the deep arterial wall of a coronary artery, at a site consistent with the previously-placed intracoronary stent, is created by laser or radiofrequency ablation, or like techniques, while being viewed through standard radiologic techniques. Once this channel appears to have been created, radio-opaque dye can be injected into the channel via a port on the intraventricular catheter. Once this radio-opaque dye, visualized by standard angiographic techniques, is seen to flow into the coronary artery at the chosen bypass site, ablation or like techniques of the heart chamber wall is discontinued.
As a third step, the catheter, which is at rest within the ascending aorta, is re-inserted into the coronary artery and advanced under standard radiologic visualization until it is again located at the site of the previously-placed intracoronary stent. The balloon on the tip of the catheter is then re-inflated. The inflation of this balloon serves two purposes. First, in the case where there is no cardiopulmonary bypass, the inflation of this catheter prevents blood from flowing from the coronary artery, through the channel formed in the second step described above, and into a chamber of the heart. To facilitate the supply of blood to the microcirculation normally fed by the coronary artery being bypassed, there are channels within the proximal and distal aspects of the intracoronary catheter. These channels allow blood within the coronary artery to enter the catheter upstream from the balloon and to flow within the catheter downstream and exit from the catheter through channels located within the catheter but distal to the balloon. The second function served by inflation of this balloon is as a physical stop for the intraventricular catheter located within the formed channel, as outlined below.
As a fourth step, the intraventricular catheter is advanced to come to rest against the wall of the inflated balloon located on the tip of the intracoronary catheter. A balloon located on the distal tip of the intraventricular catheter is then inflated. Inflation of this balloon results in the seating of a an apparatus which circumferentially surrounds this balloon against the walls of the formed channel. In one embodiment, this device can be a spiral sheet. In this embodiment, inflation of the balloon of the intraventricular catheter results in this spiral sheet being forced into an expanded position; where it takes the form of a hollow tube. In this embodiment, once this spiral sheet is forced into the form of a hollow tube, an interlocking lip on this device results in the locking of the former spiral sheet into a hollow tube configuration. In another embodiment, the expansion of the balloon on the tip of the intraventricular catheter results not only in the apparatus seating against the walls of the formed channel, it also results in the interlocking of the apparatus with the intracoronary stent previously placed. In either embodiment, the proper positioning of the intraventricular catheter tip to facilitate proper positioning of the device within the formed channel, and to result in the interlocking with the intracoronary stent if chosen, can be determined by standard radiologic techniques prior to the inflation of the intraventricular balloon. Once the device is properly postitioned and locked within the formed channel, the balloon on the tip of the intraventricular catheter is deflated. The intraventricular catheter is then withdrawn from the body.
As a fifth step, a third catheter is inserted into the innominate or femoral artery and fed retrograde through the ascending aorta and into a chamber of the left side of the heart via standard catheterization techniques. In a preferred embodiment, the third catheter is advanced into the left ventricle.
The distal tip of this third catheter holds an apparatus which has the ability to be mechanically interlocked with the first apparatus which was placed within the formed channel in the fourth step described above. The second apparatus is place within the lumen of the fromed channel through manipulation of the intraventricular catheter by standard catheter-control techniques.
In one embodiment the second apparatus can be secured to the walls of the channel itself through stapling, biologically-effective glueing, or the like. In another embodiment, this second apparatus can be interlocked with the first apparatus previously placed through various conventional techniques by which one hollow tube is mechanically locked to another hollow tube. In one embodiment, this interlocking could take the form of threading. In another embodiment, this interlocking could be accomplished by a tongue on the second apparatus that slips into a groove on the first apparatus.
The second apparatus allows blood to flow within the lumen of the apparatus either bidirectionally, or unidirectionally. In one embodiment, the second apparatus can be equipped with a check valve which allows blood to flow from a chamber of a heart into a coronary artery, while prohibiting blood flow in the opposite direction. In this embodiment, this flow-restrictive apparatus is placed within the laser-ablated channel and associated with the previously-placed apparatus.
Once the second apparatus has been located within the formed channel, and either effectively secured to the channel walls, or effectively secured to the first apparatus, the second apparatus can be released from the tip of the third catheter. In one embodiment, proper interlocking of the second apparatus to the first apparatus can be ascertained by standard radiographic techniques. In another embodiment, proper interlocking of the second apparatus to the first apparatus can be indirectly viewed through a remote fiberoptic viewing system, or the like, inherent to the third catheter. The third catheter is then withdrawn from the body.
As a sixth step, blood flow from a chamber of the heart into the bypassed coronary artery and, in cases where a check valve has been placed, the corresponding absence of flow from the coronary artery into a chamber of the heart, can be determined by standard angiographic techniques.
Clarification of Meanings
Living biological organisms react in a range of varying ways to foreign materials. The term foreign materials is meant to include all materials, whether biological or non-biological, which are not normally present within that particular subject.
Because subjects respond to foreign materials in a range of various ways, the apparatus of the present invention can be exposed to cells, treated by biological compounds, or exposed to pharmaceutical or other chemical agents, which reduce the reactions normally resulting when foreign bodies are internally introduced.
With regard to the specification and claims of this application, the phrase xe2x80x9creduce reactionxe2x80x9d is meant to indicate a reduction in tissue responses. This is meant to include, but not to be limited to, immune reactions, tissue scarring, blood clotting, and the like. The literature is replete with pharmaceuticals which can be either locally or systemically administered and which decrease the immune response to foreign bodies. These include corticosteroids, and the like. It is also well known in the literature that there are pharmaceutical agents which reduce scar tissue formation following injury. Newer published techniques to reduce re-stenosis in transplanted artificial vessels include coating such devices with non-immunogenic endothelial cells or fibroblasts. A common problem with transplanted vessels is blood clotting, and agents which reduce such clotting have been widely reported.
The phrase xe2x80x9creduce reactionxe2x80x9d is also meant to indicate a reduction in the changes in arterial walls associated with the family of diseases known as arteriosclerosis. Arteriosclerosis is the most common cause of coronary artery occlusion and/or narrowing. Pharmaceutical agents which inhibit the formation of arteriosclerotic plaques have been discovered. Coating the device with agents which decrease the accumulation of such deposits can be beneficial in the prevention of re-stenosis.
Conclusion
In summary, creating a channel or channels which lead directly from a chamber of the heart into the coronary arterial vasculature should decrease the morbidity and mortality of bypass surgery, should reduce post-surgical recovery time, should decrease coronary artery bypass grafting costs, and should allow the creation of multiple bypass sites to multiple diseased coronary arteries either simultaneously, or at some later point in time. In no way is the procedure limited by the availability and patency of veins or arteries harvested from the bypass patient. In addition, the invention eliminates the risk of aneurysmal dilitation and subsequent functional deterioration of transplanted saphenous veins, as well as the risk of arterial constriction and subsequent functional deterioration of internal thoracic or gastroepiploic arteries, particularly when compared to techniques which result in torsion on transplanted artery.